Cutting elements such as shear cutters for rock bits, for example, typically have a body (or substrate), which has a contact face. An ultra hard layer is bonded to the contact face of the body by a sintering process to form a cutting layer sometimes referred to as a “cutting table”. The body is generally made from tungsten carbide-cobalt (sometimes referred to simply as “tungsten carbide” or “carbide”), while the ultra-hard layer is a polycrystalline ultra hard material layer, such as polycrystalline diamond (“PCD”) or polycrystalline cubic boron nitride (“PCBN”). There is typically a matrix of binder material within the polycrystalline material.
Common problems that plague cutting elements having an ultra-hard material layer such as PCD or PCBN bonded to the carbide substrate, are chipping, spalling, partial fracturing, cracking or exfoliation of the cutting table. These problems result in the early failure of the ultra-hard layer and thus, in a shorter operating life for the cutting element. Typically, these problems may be the result of peak (high magnitude) stresses generated on the ultra-hard layer at the region in which the layer makes contact with an external surface, such as when the cutting layer makes contact with earthen formations during drilling. For example, generally, cutting elements are mounted onto a drag bit body at a negative rake angle. Consequently, the region of the cutting element that makes contact with an earthen formation includes a portion of the ultra-hard material layer upper surface circumferential edge. This portion of the layer is subjected to the highest impact loads.
The ultra hard material layer is generally formed of a plurality of particles compacted and sintered together. It is desirable to improve the abrasion resistance of the ultra hard material layer. Increasing the abrasion resistance of PCD materials for example, is desirable as it allows the user to cut, drill or machine a greater amount of the workpiece without wear of the cutting element. Historically, an increase in abrasion resistance has been achieved by reducing the grain size of the PCD. Toughness is sacrificed, however, as finer-grained PCD materials are less robust and more prone to chipping than coarser grades. Accordingly, much of the research into shear cutter type cutting elements has focused on making a more durable, abrasion-resistant ultra hard material layer, as well as making a better interface between the ultra hard material layer and the substrate.
It is also important that the substrate of the cutting element be durable. One common substrate material is cemented tungsten carbide. Cemented tungsten carbide generally refers to tungsten carbide (“WC”) particles dispersed in a binder metal matrix, such as iron, nickel, or cobalt, often referred to as a “WC/Co” system. Tungsten carbide in a cobalt matrix is the most common form of cemented tungsten carbide, which is further classified by grades based on the grain size of WC and the cobalt content.
Another common problem that plagues cutting elements having an ultra hard material layer bonded to a carbide substrate is the formation of extremely large, undesirable carbide grains along the interface formed between the carbide substrate and the ultra hard material layer. This is particularly true of tungsten carbide grains when the favored substrate of WC/Co is used. If not controlled, tungsten carbide grains having grain sizes in the tens and hundreds of microns, may form at the interface between the tungsten carbide substrate and the ultra hard material layer. The presence of such WC particles may cause stress fractures and the early delamination of the ultra hard material layer from the substrate. It is therefore desirable to suppress the formation and incidence of WC grains at the interface.
Accordingly, there exists a need for improving various characteristics of the ultra hard material layer, such as abrasion resistance, without compromising other characteristics of the ultra hard material layer. Correspondingly, there exists a need for a manufacturing process for forming cutting elements and the like, which include such improved characteristics.